The Ivorian turned in Valentin Stocker's cross to cancel out an early goal by Italian Federico Piovaccari, who has spent most of his career playing for Italian lower league clubs and is on loan from Sampdoria.
The draw left Basel, who began their campaign with a spectacular 2-1 win at Chelsea, with five points from four games in Group E.
Steaua, who extended their winless run in the competition to 21 games, have two points.
Steaua went ahead in the 17th minute when Lukasz Szukala sent a long pass over the Basel defence and Piovaccari broke clear to fire the ball into the roof of the net from close range.
Mohamed Salah had a couple of chances to equalise, though Steaua were closer to a second when a Florin Gardos close-range header was superbly saved by Yann Sommer.
Apart from those efforts, the Egyptian was largely kept quiet by a dogged Steaua defence.
The 1986 champions appeared to have the points in the bag until Sio escaped the attention of the defence and stretched to meet Stocker's cross.
(Writing by Brian Homewood, editing by Stephen Wood)
Share
